It is known that installations for continuous casting between rolls include two rolls with horizontal and parallel axes, vigorously cooled internally by circulation of water driven in rotation in opposite directions and spaced apart by a distance corresponding to the desired thickness of the cast product.
During casting, molten metal poured into the casting space defined between the rolls solidifies in contact with these rolls and is extracted downwards, as the rolls rotate, in the form of a thin strip. In order to contain molten metal, the side dams are pressed flat against the front ends of the rolls. Such side dams are commonly made of refractory material, at least in the part of the dam which is brought into contact with the molten metal.
It is therefore necessary to ensure leaktightness between the rolls and the side dams. For this purpose, these side dams are pressed against the ends of the rolls and, in order to reduce the friction induced during rotation of the rolls, lubrication of the interface between the rolls and side dams is usually provided. Lubrication is carried out by supplying a consumable lubricant or by using a self-lubricating material at this interface.
However, actually producing this leaktightness and retaining it throughout the casting still raises numerous difficulties, due in particular:
to the geometrical deformations of the rolls and of the side dams, in particular at the start of casting, which are caused by expansions of the various elements of the installation,
to the forces exerted on these elements in particular the forces exerted on the side dams by the cast metal in the axial direction of the rolls, which forces tend to separate the side dams from the rolls,
to wear of the side dams or of the edges of the cooled walls of the rolls, which is not always uniform over the entire area of the contact zones,
to the possible beginning of infiltration of cast metal between side dam and roll, and solidification of these infiltrations which tends to separate one from the other.
It has already been proposed to solve these problems by causing controlled wear of the side dam, by friction of the rolls against the latter, throughout the casting. The aim is thus to regenerate the interface between rolls and side dams continuously, so as to make the contact conditions over the entire area of this interface as uniform as possible. Thus, document EP-A-546,206 describes a method according to which, before the start of casting, the side dams are pressed strongly against the rolls, in order to carry out a sort of grinding-in of these side dams by abrasion by the edges of the rolls. Then this pressure is reduced and, during casting, the side dams are continued to be moved towards the rolls at a predetermined speed in order continuously to ensure the progress of intentional wear and thus to attempt to retain uniform contact over the entire area of the interfaces.
However, this method leads to a significant wear of the refractory material of the side dams, even when the contact conditions are satisfactory.
If, instead of regenerating the interface as indicated above, the side dam is merely applied with a predetermined force, stronger wear may occur in certain zones of the interface, or in other zones of localized infiltration between the edge of the rolls and the side dam, which lead to local creation of play between the roll and the side dam. For example, an infiltration of molten metal between a roll and a side dam will tend, by solidifying, to separate the side dam from the edge of the roll, and therefore also from the edge of the second roll, since the entire side dam will then be displaced backwards, with the risk of deteriorating the leaktightness at the second roll. The same problem may occur if the front end of the rolls are not perfectly orthogonal to the axes of the rolls and/or are not exactly in the same plane; in this case, the side dam is correctly applied against one roll but not against the other.